The present invention relates to a method of and apparatus for controlling the idling speed of an internal combustion engine.
A known method of controlling the idling speed consists of adjusting the position of a throttle valve or a flow-control valve in a throttle valve by-pass intake passage, by using a valve-control motor, such as a step motor or a servo motor, in feedback response to the running speed when the engine is idling.
According to the conventional control method of this type, the feedback control is immediately started when the operating condition of the engine becomes a predetermined idling condition. The predetermined idling condition exists when the throttle valve is at the idling position and the running speed of a vehicle is nearly zero. However, the rotational speed of the engine is not immediately stabilized just after the predetermined idling condition is established; the engine usually runs at a relatively high speed for a while due to the moment of inertia and then runs at a gradually decreasing speed. Therefore, if the feedback control is initiated immediately after the predetermined idling condition is established, as has been done in the conventional art, a so-called undershoot phenomenon takes place in which rotational speed abruptly decreases. In the worst case, the engine stalls.